Data hiding is a technique for embedding information into digital content without causing perceptional degradation. A special case of data hiding is steganography, which is the science and art of secret communication. In steganography, the presence of a hidden message typically needs to be concealed. This may be achieved using a stegatone. A stegatone is a data-bearing steganographic halftone, wherein data is embedded in a halftone image by shifting certain output pixel values, e.g. from 0 to 1. Another case of data hiding is watermarking, where it may be desired to determine the authenticity of digital content. In this case, the presence of a covert watermark may indicate authenticity, while the absence of a watermark may indicate a forgery. When watermarking a document there may be a challenge of avoiding an active adversary that would attempt to remove, invalidate or forge watermarks in digital content. Shifting pixel values of an output halftone may also be used for fragile watermarking. For example, portions of digital content may be modified without causing perceptional degradation such that a proportion of white (e.g. 0 value) or black (e.g. 1 value) in a particular portion is over a predefined threshold.